Michael Bender’s group measures oxygen and argon in the atmosphere and ocean surface waters to gain insight into interannual variability of carbon sinks and the spatial and temporal variability of biological productivity.
Deployment of atmospheric autosamplers
The measurement of the O2/N2 ratio of air provides a tool for tracking global CO2 uptake by the land biosphere as well as by the ocean, and reflects the fertility of ecosystems on the scale of ocean basins. Since the inception of the grant, the group has built multiple automated sampling devices that are significantly increasing the accuracy of atmospheric argon and oxygen records. In previous years, automatic samplers had been installed at in the Equatorial Pacific, Tasmania, Samoa, Barrow, and Sable Island (in the Northwest Atlantic) for measurement of oxygen-nitrogen ratios.
This year automated samplers were installed at additional sampling sites, including Macquarie Island in the Southern Ocean (reached by a long journey on a supply ship). In addition, the database program and data processing routine for calculating O2/N2 and Ar/N2 ratios from the analytical data are now automated. The automation is a major improvement that allows easy visualization of the standard and sample results easily and assures excellent quality control.
The Bender team has used O2/N2 data to make increasingly reliable estimates of the size and variability of the land and ocean carbon sinks. Most independent evidence suggests that ocean uptake is roughly constant, with the land biosphere accounting for most of the interannual variability in the global CO2 sink. However, observations of oxygen concentration in the atmosphere over the last several years suggest that there have been large interannual variations in ocean CO2 uptake.
To help resolve the discrepancy in land sink variability estimates, this year the Princeton O2/N2 record was analyzed to assess the partitioning of fossil fuel CO2 between ocean uptake and uptake by the land biosphere. From 1994–2002, the average CO2 uptake by the ocean and the land biosphere was 1.7 ± 0.5 and 1.0 ± 0.6 GtC/yr respectively. Very strong covariance between CO2 sequestration by the land biosphere as calculated from O2/N2 data with independently calculated total sequestration supports earlier conclusions that most interannual variability in CO2 uptake is due to the land biosphere.
Measuring ocean productivity
Jan Kaiser recently developed a new device to measure oxygen and argon supersaturation in ocean surface waters to monitor biological productivity. The new mass spectrometer allows rapid and continuous sampling of surface seawater intake on board a ship, rather than requiring that individual samples be brought back to a laboratory on land for analysis. The efficiency of the device has allowed the group to make high resolution measurements of the variability of marine biological activity in space and time, which makes it a valuable tool for understanding the details of the modern carbon cycle.
After two equatorial cruises, this year Nicolas Cassar used the instrument on a Southern Ocean cruise. The results confirm earlier findings that net production is highest at the northern boundary of the Southern Ocean, a result we attribute to the supply of nutrient iron by windblown dusts from Australia, South America, and Africa.